You are always flagged for PvP, except in a few Sanctuary spots, like Dalaran/Shattrath I believe.

You can get ganked in your own home city and in every levelling area.

Not true,you can only get ganked in contested territories.If you are horde on horde territory or alliance on ally soil you can only be attacked after you attack them first..They will be yellow to you and while you can attack them they can NOT attack you,same in the faction capitals.On contested territory though you are correct,they can and will gank the crap outta you,doesn't really matter than blizz changed it so players below level 10 doesn't give honor (like that stopped anyone to begin with...) Some quests with a pvp tag on them gets you pvp flagged though even on your own factions soil,check your portrait,if you have a horde/alliance logo under it youre pvp flagged.If you are on non contested territoty you can just log out and back in to remove it.